The subject matter of this application is directed to magnetic circuits implemented on an integrated circuit for providing functionality derived from magnetic circuits, e.g., applications for resistor-inductor-capacitor (commonly, “RLC”) circuits.
Traditional switched power converters require discrete inductors that are large and expensive. For many portable applications such as handsets, size and cost are critical. For a single battery system, there are usually many voltage domains so that power is optimized for each voltage domain. Such systems require efficient power conversion from the voltage of the source battery to the other voltage domains to optimize power consumption and thus extend battery life. Linear regulators can be used without the need of inductors, but they are very inefficient, especially for large step down ratios. It is desired to have switched converters for step down and step up conversions for efficient power transfer, however, discrete inductors required for the switching power converters are large and heavy, not desirable for portable applications. Also, for portable applications, it is desired that the converters have good load transient response and thus fast switching frequency. Discrete inductors are disadvantageous for such applications because they become lossy at high frequencies. It is desired to have inductors that are small, light weight and have good high frequency efficiency.
Air core inductors have limitations due, in part, to high resistance and low inductance. For example, power may be radiated back to the power plant or ground plane which may affect the electromagnetic interference (EMI). Designers must concentrate a great deal of effort to using high frequency signals and switching to mitigate the effects of EMI. EMI is proportional to frequency. Printed circuit board (PCB) designers must be concerned with EMI effects due to high currents that are generated. Radiated power is also a problem as it may interfere with other circuits that are not connected to the PCB.
In addition, when manufactured within an integrated circuit die (“IC”), air core inductors are not efficient with small inductance and high resistance, which causes users to limit power available due to thermal limits for packaging. On chip power dissipation limits the power that may be provided to an on-chip inductor. These effects can limit the applications for which air core IC inductors can be used.
The addition of magnetic cores to inductors increases winding inductance and power conversion efficiency resulting in lower inductor peak current, reduced power consumption and also reduced interference to other components. It can lead to use of lower switching frequencies among driving signals. Further, magnetic flux is more constrained by a magnetic core which limits EMI corruption to circuit components that would be co-located with the magnetic core inductor. Increased inductance per unit area also leads to high energy density and device miniaturization.
Magnetic core-based inductors have been used on integrated circuit dies with only limited success. Usually planar spiral coils are used with the addition of a single magnetic layer above or below them. The inductance enhancement from such implementation over the air core spirals is very limited, at most 100%. To achieve the inductance needed, it occupies a large die area. Its size mismatch with power switching circuits makes the integration not economically viable. Magnetic core-based inductors tend to occupy large areas when laid out on integrated circuit die, which interferes with design attempts to make smaller chips. Such layout issues become exacerbated when designers attempt to find configurations that allow such integrated circuits to be mounted on larger components, for example, a printed circuit board (PCB). No known inductor configuration adequately meets these design needs.